1. Field of the Invention
The present invention relates to a semiconductor device and manufacturing method thereof, and more particularly, to a semiconductor device employing a fluorine-doped silicon oxide layer as an interconnection insulating layer, and a method of manufacturing the same.
2. Description of the Related Art
In prior art semiconductor devices, SiO2 layer has been used as an insulating layer to electrically isolate interconnections. Such an SiO2 layer is primarily produced from source gas, for example, silane (SiH4) and tetraethoxysilane (TEOS) by a low pressure or atmospheric pressure chemical vapor deposition (CVD) technique. Particularly, plasma chemical vapor deposition can produce an SiO2 layer at a low temperature of about 400° C., using TEOS and O2, and the SiO2 layer produced in this way has been widely used. Further, as compared with other thin layer producing methods, the CVD method often uses high purity gas as a reaction source, and provides high quality layers.
However, as microstructure of semiconductor elements has become widespread in recent years, concern about reduction of signal transmission speed has arisen. This implies a problem that reduced interconnection space increases the capacitance between interconnections and reduces signal transmission speed. The reduction in signal transmission speed seems to be one of the negative factors in increasing the performance of semiconductor devices. Therefore, to solve the problem, it is essential to reduce permittivity of the insulating layer formed between interconnections to the lowest possible value.
To reduce the permittivity, in recent years, fluorine-doped silicon oxide or fluorine-doped silicate glass (FSG) has been developed together with the parallel plate CVD technique or high density plasma CVD technique (HDP-CVD). As a method of producing high-density plasma, use of electron cyclotron resonance (ECR) or the inductive coupled plasma (ICP) coil or helicon wave, for example, has been reported.
FIG. 1 shows a sectional view of Cu multi-layer interconnection using a conventional FSG layer. In the same drawing, reference number 81 indicates an FSG layer and likewise, 82 indicates a barrier metal layer, 83 indicates a Cu interconnection in a lower layer, 84 indicates a silicon nitride layer, 85 indicates an FSG layer, 86 indicates another barrier metal layer, 87 indicates a Cu interconnection of an upper layer, 88 indicates another silicon nitride layer and 89 indicates a silicon substrate, respectively. The Cu interconnections 83 and 87 are dual damascene interconnections.
In the FSG layer, as has been reported, the higher the fluorine (F) density, the lower the permittivity, and at the same time, moisture absorption increases. As the moisture absorption of FSG layers 81 and 85 increases, moisture (H2O) is taken into these FSG layers. And, H caused by the moisture reacts with F contained in these FSG layers, and HF is liberated from the FSG layers 81 and 85.
Even if moisture is not taken in, HF is produced from H that is inherently contained in the FSG layer 81. Furthermore, HF is also produced by reaction of hydrogen (H) and moisture (H2O) in silicon nitride layers 84 and 88 with surplus fluorine (F) in FSG layers 81 and 85. FSG layers 81 and 85 and silicon nitride layers 84 and 88 contain H, because gaseous materials such as silane and ammonia containing H are employed as source gas, and this H is mixed into FSG layers 81/85 and silicon nitride layers 84/88.
The above-noted HF will cause corrosion of Cu interconnections 83/87 or barrier metal layers 82/86, and degrade adhesion between Cu interconnections 83/87 and insulating layers 81/84/85/88. Further, this corrosion and deteriorated adhesion will cause more serious problems, for example, layer peeling off, bonding durability decline and decrease in reliability.
As described above, it has been proposed to use an FSG layer in interconnections as an insulating layer with low permittivity, to prevent signal transmission delay. However, there is a problem in using an FSG layer, that is, moisture absorption is high and HF is generated, causing corrosion of interconnection itself or barrier metal layer or peeling off of layers. Thus, a semiconductor device employing fluorine-doped silicon oxide as an insulating layer for interconnections and including multi-layer interconnection to decrease the influence of HF, and a method of manufacturing the same have been expected.